Long term effects of limp mode?

[macNcheese]

I bought my first S4 about 9 months ago. It didn't have a boost gauge, and I had no experience with these cars beforehand. Turns out it has been in limp mode the whole time. Bad EGT's which weren't found using an OBD. I'm replacing them once my new DP's arrive. Are there any catastrophic issues from driving it in limp mode this long? Aside from me feeling like an idiot.

[Jism]

No. Limp = safety precautions.

Able to make it to the dealer and all without doing harm towards your engine. All resets to absolute safe values.

[getslideways]

In general, yes that is what limp mode is for, to protect against swift catastrophic damage. However, limp mode is designed to "limp" you to a dealer or service station, not intended to be used as a daily driving configuration. For example:

The OP mentioned EGT failure, one of the often "safe modes" for this situation is for the ECU to dump excessive amounts of fuel into the engine in an attempt to cool what it thinks may be high EGTs. However all that excess fuel is not great for the stock cats, plugs, and sensors (which sounds like cats may not be an issue with new downpipes ) However, this is not a "catastrophic" situation, but could be a costly one if needing to replace factory cats at a result. I only mention this as I dont want others to read this and assume "its a perfectly fine idea to knowingly and intentionally drive in limp mode for excessive and and extended periods of time". However, again, its a case by case scenario, greatly depending on what is triggering the limp mode in the first place, and as Jism said, intended to just get you to a dealer or service station.

So chances are the OP is fine, but its not exactly great to continually be using limp mode, as some event is taking place for the ECU to cause it. So whatever that event is, is still happening after each restart prior to re-triggering the limp condition (knock, misfire, overboost, underboost, etc)

[james 408]

Slideways is dead on.

I'll add: this happens all the time. Half the audi/vws on the road from our generation are probably in limp mode as we speak.

[getslideways]

Half the audi/vws on the road from our generation are probably in limp mode as we speak.

the other half are on jackstands indefinitely

[Jism]

Unless you can actually afford and maintain a proper S4 or RS4, no limp going on at all. :)